When drilling a material to be cut which exhibits high ductility, such as stainless steel and mild steel, that is, a material with high toughness by a cutting edge replaceable drill, a long continuous chip is likely to be generated. The long chip is not preferable because of the following reasons.
The long chip is likely to be entangled with a drill body, and the chip entangled with the drill body may close the opening of a chip discharge groove (flute). If the chip discharge groove is clogged with the chip, it is difficult to continue further cutting. If the chip is further entangled with the drill body, the chip may damage a workpiece, that is, work. Therefore, if the long chip is entangled with the drill body, the processing is interrupted and an operation of removing the entangled chip is generated. Such an operation deteriorates the productivity. Furthermore, the long extended chip has a heavy weight, and accordingly such scattering of chips caused, for example, by rotation of the drill is unfavorable in a safety aspect. Additionally the long extended chip is unfavorable for the operation of the peripheral machine. For example, such chip may interrupt the operation of the conveyor, which also affects the productivity.
Patent Literature 1 discloses the tip for drill, that is, cutting insert originated to allow use in the process of cutting the mild steel and stainless steel, and having a center edge that constitutes a center portion of an end cutting edge, and a peripheral edge that constitutes the outer circumferential part of the end cutting edge. This cutting insert has a substantially parallelogram plate shape. The center edge and the peripheral edge are arranged and formed on the edge of the upper surface of the substantially parallelogram shape via the corner part. A breaker groove with the shape of concave curved surface is formed in the upper surface along the center edge and the peripheral edge. The breaker groove of the peripheral edge is larger than the breaker groove of the center edge with respect to both the length and depth in the direction orthogonal to the cutting edge. As a result, on the peripheral edge, it is intended to favorably curl the chip to suppress long extension of the chip, and on the center cutting edge, it is intended to suppress rapid increase in the cutting resistance by avoiding clogging with the chip.